As the information industry develops, large-volume information processing is required, and demand for information storage media capable of storing a large amount of information is continuously increasing. A hard-disk drive (HDD), which is widely used as information storage medium, generally includes a read/write head and a rotating medium on which information is recorded, and can store large amount of information of 100 GB or more. However, a storage device having a rotating part such as an HDD tends to be worn out, and there is a disadvantage in that reliability is low due to a possibility of occurrence of an error during operation.
In recent years, researches and developments have been made on a new data storage device using the principle of magnetic domain wall movement of magnetic materials. In general, a magnetic micro domain constituting a magnetic structure is called a magnetic domain. In one magnetic domain, it is characterized in that the rotation of electrons, that is, the magnetic moment, is in the same direction. The size and magnetization direction of the magnetic domain can be appropriately controlled by the shape, size and external energy of the magnetic material. The magnetic domain walls represent the boundaries of magnetic domains having different magnetization directions. The magnetic domain wall is characterized in that it can be moved by a magnetic field or a current applied to the magnetic material.
Meanwhile, if the width of a magnetic thin film is reduced to form a ribbon-like structure, the magnetization state can be uniformly formed in the width direction, and it can be used as a memory device when matched to “1” or “0” depending on the state of the magnetic domain. This type of memory is called a magnetic domain wall racetrack memory. In order to operate the magnetic domain wall racetrack memory device, it is necessary that all the magnetic domain walls move uniformly in the longitudinal direction of one device. The magnetic domain wall can be moved by using a magnetic field or electric current. Meanwhile, recently, a lot of studies have been made on a method for moving magnetic domain walls by flowing electric current.
However, if electric current that is sufficient for moving magnetic domain walls is supplied to a memory device, the problem of temperature increase due to Joule heating caused by the electric current becomes so serious that the memory device is destroyed. In addition, although the magnetic domain wall can be moved by using a magnetic field uniformly applied from the outside, it is problematic that the magnetic domain wall cannot be used since it only moves away or comes closer without uniformly moving in one direction.
Furthermore, another method using a magnetic field has recently been proposed. A device is oriented such that magnetic domain walls move in only one direction and the directionality of the magnetic domain wall of the device is determined by forming a device with asymmetric serration or by post-processing. When a magnetic field is applied to such an asymmetric sample such that the direction of the magnetic field continuously changes in the positive or negative direction, the magnetic domain wall moves in one direction while reciprocating. This method has a disadvantage in that a complicated process is required to orient the device.